IEC 60695 6 1 Edition 2 1 2010 09 INTERNATIONAL STANDARD NORME INTERNATIONALE Fire hazard testing – Part 6 1 Smoke obscuration – General guidance Essais relatifs aux risques du feu – Partie 6 1 Opacit[.]
Terms and definitions
For the purpose of this document, the terms and definitions and symbols given in ISO/IEC
13943, some of which are reproduced below for the uses’ convenience, as well as the following apply
3.1.1 combustion exothermic reaction of a substance with an oxidizer
NOTE Combustion generally emits effluent accompanied by flames and/or visible light
3.1.2 extinction area of smoke product of the extinction coefficient and the volume occupied by the smoke
NOTE It is a measure of the amount of smoke
3.1.3 extinction coefficient of smoke natural logarithm of the opacity of smoke divided by the path length of the light used to measure the smoke opacity
3.1.4 fire a) process of combustion characterized by the emission of heat and effluent accompanied by smoke, and/or flame, and/or glowing; b) rapid combustion spreading uncontrolled in time and space
3.1.5 fire effluent total gaseous, particulate or aerosol effluent from combustion or pyrolysis
3.1.6 fire hazard potential for injury or loss of life and/or damage to property by fire
3.1.7 fire model a laboratory process, including both the apparatus and the mode of operation, intended to simulate a certain stage of a real fire
This section provides a comprehensive overview of the fire scenario, detailing the environmental conditions and various stages from pre-ignition to the conclusion of combustion It focuses on a specific location or a real-scale simulation to illustrate the dynamics of an actual fire event.
3.1.9 flash-over the rapid transition to a state of total surface involvement in a fire of combustible materials within an enclosure
3.1.10 heat flux amount of thermal energy emitted, transmitted or received per unit area and unit time
NOTE It is expressed in watts per square metre
NOTE The term "ignition" in French has a very different meaning [state of body combustion]
3.1.12 large scale test a test, the size of which exceeds that of a typical laboratory bench test
The mass optical density of smoke is calculated by multiplying the optical density by the factor \( \frac{V}{L \times \Delta m} \), where \( V \) represents the volume of the test chamber, \( \Delta m \) denotes the mass loss of the test specimen, and \( L \) is the light path length.
3.1.14 opacity (of smoke) the ratio (I/T) of incident luminous flux (I) to transmitted luminous flux (T) through smoke, under specified test conditions
3.1.15 optical density (of smoke) [lg( I / T )] common logarithm of the opacity of smoke (see also specific optical density)
3.1.16 realscale test a test which simulates an end-use situation in both size and surroundings
3.1.17 small scale test a test which may be made on a typical laboratory bench
3.1.18 smoke a visible suspension of solid and/or liquid particles in gases resulting from combustion or pyrolysis
3.1.19 smoke obscuration the reduction in visibility due to smoke
3.1.20 smoke production rate extinction area of smoke produced, per unit time, by the combustion of a material under specified test conditions
3.1.21 smoke release rate see "smoke production rate"
3.1.22 specific extinction area of smoke extinction area of smoke divided by the mass loss of the test specimen
The specific optical density of smoke is calculated by multiplying the optical density by a geometric factor, represented as \$\frac{V}{AL}\$, where \$V\$ denotes the volume of the test chamber, \$A\$ is the exposed surface area of the test specimen, and \$L\$ is the light path length.
The term 'specific' in this context refers to a dimensionless quantity linked to a specific test apparatus and the exposed surface area of the test specimen, rather than indicating 'per unit mass'.
3.1.24 visibility maximum distance at which an object of defined size, brightness and contrast can be seen and recognized
3.1.1 combustion exothermic reaction of a substance with an oxidizing agent
NOTE Combustion generally emits fire effluent accompanied by flames and/or glowing
3.1.2 extinction area of smoke product of the volume occupied by smoke and the extinction coefficient of the smoke
NOTE It is a measure of the amount of smoke, and the typical units are square metres (m 2 )
3.1.3 extinction coefficient natural logarithm of the ratio of incident light intensity to transmitted light intensity, per unit light path length
NOTE Typical units are reciprocal metres (m –1 )
〈general〉 process of combustion characterized by the emission of heat and fire effluent and usually accompanied by smoke, flame or glowing or a combination thereof
In English, the term "fire" encompasses three distinct concepts, with two of these referring to specific types of self-sustaining combustion Notably, these concepts are represented by different terms in both French and German.
〈controlled〉 self-supporting combustion that has been deliberately arranged to provide useful effects and is limited in its extent in time and space
〈uncontrolled〉 self-supporting combustion that has not been deliberately arranged to provide useful effects and is not limited in its extent in time and space
3.1.7 fire effluent totality of gases and aerosols, including suspended particles, created by combustion or pyrolysis in a fire
3.1.8 fire hazard physical object or condition with a potential for an undesirable consequence from fire
3.1.9 fire model fire simulation calculation method that describes a system or process related to fire development, including fire dynamics and the effects of fire
3.1.10 fire scenario qualitative description of the course of a fire with respect to time, identifying key events that characterise the studied fire and differentiate it from other possible fires
The article outlines the key phases of fire dynamics, including the ignition and growth of fire, the fully developed fire stage, and the decay phase It also emphasizes the environmental factors and systems that influence the progression of a fire.
〈stage of fire〉 transition to a state of total surface involvement in a fire of combustible materials within an enclosure
3.1.12 heat flux amount of thermal energy emitted, transmitted or received per unit area and per unit time
NOTE The typical units are watts per square metre (Wãm –2 )
〈flaming combustion〉 initiation of sustained flame
3.1.15 large-scale fire test fire test, that cannot be carried out in a typical laboratory chamber, performed on a test specimen of large dimensions
NOTE A fire test performed on a test specimen of which the maximum dimension is greater than 3 m is usually called a large-scale fire test
The mass optical density of smoke is calculated by multiplying the optical density of smoke by the factor \( \frac{V}{\Delta m L} \), where \( V \) represents the volume of the test chamber, \( \Delta m \) denotes the mass lost from the test specimen, and \( L \) is the length of the light path.
NOTE The typical units are square metres per gram (m 2 ⋅ g -1 )
3.1.17 obscuration by smoke reduction in the intensity of light due to its passage through smoke cf extinction area of smoke (3.1.2) and specific extinction area of smoke (3.1.26)
NOTE 1 In practice, obscuration by smoke is usually measured as the transmittance, which is normally expressed as a percentage
NOTE 2 Obscuration by smoke causes a reduction in visibility
3.1.18 opacity of smoke ratio of incident light intensity to transmitted light intensity through smoke, under specified conditions cf obscuration by smoke (3.1.17)
NOTE 1 Opacity of smoke is the reciprocal of transmittance
NOTE 2 The opacity of smoke is dimensionless
The optical density of smoke quantifies the reduction of a light beam's intensity as it travels through smoke This measurement is expressed as the logarithm to the base 10 of the smoke's opacity, providing a clear indication of how much light is absorbed or scattered by the smoke For further reference, see the specific optical density of smoke (3.1.26).
NOTE The optical density of smoke is dimensionless
3.1.20 real-scale fire test fire test that simulates a given application, taking into account the real scale, the real way the item is installed and used, and the environment
NOTE Such a fire test normally assumes that the products are used in accordance with the conditions laid down by the specifier and/or in accordance with normal practice
3.1.21 small-scale fire test fire test performed on a test specimen of small dimensions
NOTE A fire test performed on a test specimen of which the maximum dimension is less than 1 m is usually called a small-scale fire test
SMOGRA smoke growth rate parameter that is a function of the rate of smoke production and the time of smoke production
NOTE Further details are given in 6.2.4
SMOGRA index maximum value of SMOGRA during a defined test period
NOTE Further details are given in 6.2.4
3.1.24 smoke visible part of fire effluent
3.1.25 smoke production rate amount of smoke produced per unit time in a fire or fire test
NOTE 1 It is calculated as the product of the volumetric flow rate of smoke and the extinction coefficient of the smoke at the point of measurement
NOTE 2 The typical units are square metres per second (m 2 ⋅ s -1 )
The specific extinction area of smoke is defined as the ratio of the smoke extinction area produced by a test specimen over a specified time period to the mass lost from the test specimen during that same time frame.
NOTE The typical units are square metres per gram (m 2 ãg -1 )
3.1.27 specific optical density of smoke optical density of smoke multiplied by a geometric factor
The geometric factor is calculated using the formula \$\frac{V}{A \cdot L}\$, where \$V\$ represents the volume of the test chamber, \$A\$ denotes the area of the exposed surface of the test specimen, and \$L\$ indicates the light path length.
The term "specific" refers to a quantity linked to a specific test apparatus and the area of the exposed surface of the test specimen, rather than indicating "per unit mass."
NOTE 3 The specific optical density of smoke is dimensionless
3.1.28 visibility maximum distance at which an object of defined size, brightness and contrast can be seen and recognized
Symbols
A exposed area of test specimen m 2
(commonly called optical density per metre) m –1
D mass mass optical density m 2 kg –1
D maximum specific optical density dimensionless
I / ratio of incident light to transmitted light dimensionless k linear Napierian absorption coefficient
L light path length through smoke m Δ m mass loss of test specimen kg m & mass loss rate kg s –1
S smoke extinction area (also total smoke) m 2
(rate of change of extinction area) m 2 s –1 t time s Δ t sampling time interval s
V & volume flow rate of smoke m 3 s –1 σ f specific extinction area m 2 kg –1 γ a constant of proportionality between visibility and extinction coefficient dimensionless ω visibility m
NOTE 1 The quantities based on log 10 , i.e D , D ′, D max, D mass and Ds, have similar symbols but they are different quantities and have different units
NOTE 2 The use of the term "specific" in the case of specific optical density, Ds, does not denote "per unit mass"
4 General aspects of smoke test methods
Fire scenarios and fire models
Recent advancements in fire effluent analysis have highlighted that the composition of combustion products is significantly influenced by the materials being burned, temperature, and ventilation conditions, particularly oxygen availability Table 1 illustrates the relationship between various fire stages and atmospheric changes This table can be utilized to establish laboratory test conditions that closely mimic real-scale fire scenarios.
Fire encompasses a complex interplay of physical and chemical processes, making it challenging to replicate all characteristics of a full-scale fire in smaller testing setups This issue of fire model validity stands out as one of the most significant technical challenges in fire testing.
General guidance for assessing the fire hazard assessment of electrotechnical products is given in IEC 60695-1-1 60695-1-10
Fire development after ignition varies based on environmental conditions and the arrangement of combustible materials Generally, a temperature-time curve for fire development in a compartment can be divided into three stages, followed by a decay stage.
Stage 1 marks the initial phase of a fire before it reaches sustained flaming, characterized by minimal increases in room temperature The primary dangers during this stage are ignition and the production of smoke.
Stage 2, known as the developing fire phase, begins with ignition and culminates in a rapid increase in temperature within the fire room During this stage, the primary hazards include the spread of flames, heat release, and smoke Stage 3, or the fully developed fire phase, commences when all combustible materials in the room have decomposed sufficiently, leading to a sudden ignition throughout the space, resulting in a swift and significant temperature rise, commonly referred to as flash-over.
At the conclusion of stage 3, the combustibles and oxygen are mostly depleted, leading to a decrease in temperature This decline occurs at a rate influenced by the system's ventilation and its heat and mass transfer properties, a phenomenon referred to as decay.
Different stages of decomposition produce varying mixtures of products, which affect the density of smoke generated Additionally, understanding the fire scenario is crucial, particularly regarding incident heat flux, oxygen availability, and smoke-venting options.
Table 1 – General classification of fires (ISO/TR 9122-1)
Irradiance *** kW/m 2 Stage 1 Non-flaming decomposition a) Smouldering
21 Not applicable